چكيده به لاتين
Adhesively bonded joints have been used in many advanced non-industrial applications including dentistry and orthodontic. In common orthodontic treatments, brackets are bonded to teeth surface by using composite or nano-composite adhesives for moving teeth in the correct position. The bracket bond strength is considered as an important parameter for load bearing in a bracket/adhesive/tooth system in the orthodontic treatments. In this thesis, experimental methods in nano, micro and meso scales along with numerical simulation approach have been utilized to determine the bond strength of orthodontic bracket to tooth.
Nano-indentation and micro-indentation experiments are applied on the weakest part of the orthodontic bonding, i.e. the nano-composite adhesive, to determine the orthodontic bond strength. Subsequently, a hybrid experiment-simulation approach is developed to interpret the scattered results obtained from the nano-indentation experiment on the nano-composite that is considered as a non-homogenous material in the test scale. In this respect, the hyperelastic behavior of the polymeric matrix of the nano-composite is investigated through development of a new hybrid-experiment simulation approach. Based on the results, it is recommended that the number of indentation tests on non-homogenous samples increases more than the conventional process (i.e. 5 tests according to ISO 14577) to at least 20 times along with the use of an indenter with larger contact area compared to the Berkovich.
In the meso-scale experiment, mode I, mode II and mixed modes I/II and I/II/III debonding tests are conducted to investigate the bond strength of orthodontic bracket bonded by the nano-composite adhesive. Comparing the orthodontic bond strength values obtained from nano-indentation and micro-indentation experiments with the corresponding values measured from the meso-scale tests indicates considerable difference which means that nano-indentation and micro-indentation experiments are not appropriate for determination of orthodontic bond strength.
A direct test method is developed to determine the damage behavior of the orthodontic bonding in single modes. The results of these tests are used to adapt a cohesive zone model (CZM) and cohesive parameters for the bracket/nano-composite adhesive/tooth bonding. Then, the CZM is applied in the finite element (FE) simulation of the 3-dimensional model of the tests in the single and mixed mode conditions. Results of all simulations are examined well in order to validate the CZM, cohesive parameters and simulation process. The FE results are used to determine the orthodontic bond strength in various loading conditions and also for different shapes of the bracket base. It is concluded that, the FE simulation processes using the CZM could be applied to reduce the amount of required tests in order to determine the orthodontic bond strength in different quasi-static loads and boundary conditions.
